The enzymes, characterized from bacteria (Peptoclostridium difficile,
Enterococcus faecalis and from lactic acid bacteria) prefer
substrates with a main chain of 5 carbons (such as 4-methyl-2-
oxopentanoate) to those with a shorter chain.

It also utilizes phenylpyruvate.

The enzyme from the halophilic archaeon Haloferax mediterranei
prefers substrates with a main chain of 3-4 carbons (pyruvate and
2-oxobutanoate).